textarea 文本框自适应高度

输入文本前：

输入文本后（自适应）：

 

实现：

html:

js:

// textarea自适应高度
function makeExpandingArea(el) {
    var timer = null;
    var setStyle = function(el, auto) {
        if (auto) el.style.height = 'auto';
        el.style.height = el.scrollHeight + 'px';
    }
    var delayedResize = function(el) {
        if (timer) {
            clearTimeout(timer);
            timer = null;
        }
        timer = setTimeout(function() {
            setStyle(el)
        }, 200);
    }
    if (el.addEventListener) {
        el.addEventListener('input', function() {
            setStyle(el, 1);
        }, false);
        setStyle(el)
    } else if (el.attachEvent) {
        el.attachEvent('onpropertychange', function() {
            setStyle(el)
        })
        setStyle(el)
    }
    if (window.VBArray && window.addEventListener) { //IE9
        el.attachEvent("onkeydown", function() {
            var key = window.event.keyCode;
            if (key == 8 || key == 46) delayedResize(el);

        });
        el.attachEvent("oncut", function() {
            delayedResize(el);
        }); //处理粘贴
    }
}

var textarea = document.getElementById('textarea');
makeExpandingArea(textarea);